The present invention relates to a sheet material cutting device to cut sheet material by the cooperation of two rotary blades which travel while rotating.
In a printer for a terminal such as an ECR or a POS, strip-shaped sheet material wound into a roll is pulled out for printing, and then the necessary portion is cut by a cutter into a sheet for delivery.
Various types of such sheet material cutting device are available. A rotary cutter requires high manufacturing costs and causes a relatively high degree of noise and, therefore, is now being replaced by a cutter featuring a combination of a circular rotary cutting blade moving while rotating and a fixed cutting blade formed into a long sheet.
The prior art sheet material cutting device of this type will be described below with reference to FIG. 8A and 8B. As shown in FIG. 8A, a supporting member 101 with a rotary blade 102 travels horizontally along a screw shaft 100. In FIG. 8B, the rotary blade 102 is rotatably bearing-supported on a shaft 104 mounted on the supporting member 101 and pressed against a fixed blade 103 by means of a spring 104. In FIG. 8A again, sheet material, fed in the vertical direction to the paper on which said figure appears, is cut by the rotary and the fixed blade as the supporting member travels horizontally.
With this type of cutting device, it is important, in order to cut the sheet material sharply, that the rotary blade 102 is slightly inclined toward the fixed blade 103 as shown in FIGS. 9 and 10, so that the periphery of the rotary blade 102 comes into contact with the edge of the stationary blade at a certain point P in the traveling direction of the rotary blade. Furthermore, when one wishes to cut a sheet material by both the forward and backward travel of the rotary blade 102, a means to switch the inclination of the rotary blade between the forward and backward travel is necessary. This type of device is actually proposed in, for example, the Japanese Examined Patent No. 50-24466/1975. The drawback of this device is that switching the rotary blade is complex and expensive because the rotary blade is switched for necessary inclination by using additional components such as a wire stretched horizontally or a lever oscillating around a pivot shaft.
To solve the above problems of conventional devices, the inventors of the present invention have already proposed a sheet material cutting device as described in U.S. Pat. No. 5,307,716. This device permits satisfactory cutting of strip-shaped sheet material such as paper by simply causing the rotary blade to incline by the angle necessary for cutting, in both the forward and the backward motion of the rotary blade, by the cooperation of the circular rotary blades moving while rotating, a roller for rotating the rotary blade, and a roller guide.
However, the above device has no mechanism to prevent lifting of the sheet material when it is being cut. Thus, sheet material would be lifted from the fixed blade or bent, thus preventing satisfactory cutting. Furthermore, depending on the contact between the rotary and the fixed blade, wearing of the cutting edge of the fixed blade is not always uniform over the entire length. This also prevents satisfactory cutting of the sheet material.